Thomas Weinert has a recent post to his blog showing how to use one of the more powerful XML-handling features that PHP's DOM extension includes - XPath.
Often I hear people say "We use SimpleXML, because DOM is so noisy and complex". Well, I don't think so. This article explains how you can parse a XML (an Atom feed) using the PHP DOM extension. No other libraries are involved.
In his example he loads an external feed (his own) into a DOM object, blocks any errors with a few handy functions and creates a DOMXPath object on the DOM object to get ready for his queries. He shows how to make searches for titles, subtitles, looping over attributes and an element list returned from one of the first queries. A full code listing is also provided to show how it all fits together.